Process to produce pipeline-transportable crude oil from feed stocks containing heavy hydrocarbons

ABSTRACT

A process for the production of a pipeline-transportable crude oil from a bitumen feed, the process comprising:
     (1) dividing the bitumen feed into two fractions, the first fraction comprising between 20 and 80 wt % of the feed, the second fraction comprising between 80 and 20 wt % of the total feed, (the two fraction together forming 100 wt % of the feed),   (2) distillation of the first fraction obtained in step ( 1 ) (preferably under vacuum) into a light fraction boiling below 380° C. (preferably the 450° C. fraction, more preferably the 510° C. fraction) and a residual fraction;   (3) thermal cracking (of at least part of, preferably all of,) the residual fraction obtained in the distillation process described in step ( 2 );   (4) distillation of the product obtained in step ( 3 ) into one or more light fractions (boiling below 350° C.), optionally one or more intermediate fractions (boiling between 350 and 510° C.) and a heavy fraction (boiling above at least 350° C.);   (5) combining the second fraction obtained in step ( 1 ), the light fraction obtained in step ( 2 ) and the light fraction(s) obtained in step ( 4 ) to obtain a pipeline-transportable crude oil; and   (6) using heavy fraction obtained in step ( 4 ) for the generation of power and/or heat.

The present application claims priority to European Patent ApplicationNo. 03077061.4 filed 01 Jul., 2003.

1. Field of the Invention

The invention relates to a process for the production of apipeline-transportable crude oil from a bitumen feed, especially a tarsands bitumen, comprising separating the feed into two parts,distillation of one part to obtain a light and a heavy fraction, thermalcracking of the heavy fraction to produce one or more light fractionsand one or more heavy fractions, mixing all light fractions and thesecond part of the feed to obtain a pipeline-transportable crude oilwhich can be transported over long distance for further treatment in a(standard) refinery, and using the heavy fraction obtained after thermalcracking for the generation of heat and/or power. The bitumen feed isespecially crude oil extracted from tar sands.

2. Background of the Invention

Very heavy crude oil deposits, such as the tar sand formations found inplaces like Canada and Venezuela, contain trillions of barrels of a veryheavy, viscous petroleum. This heavy crude oil is referred to in thisspecification as bitumen. The bitumen has an API gravity (ASTM D 287)typically in the range of from 5° to 10° and a viscosity, at formationtemperatures and pressures that may be as high as a million centipoise.The hydrocarbonaceous molecules making up the bitumen are low inhydrogen and have a resin plus asphaltenes content as high as 70%. Thismakes the bitumen difficult to produce, transport and upgrade. It needsto be diluted with a solvent if it is to be transported by pipeline toan upgrading or other facility as the production location is usually ata considerable distance from the upgrading facility. A process forproducing a diluent for transporting the bitumen upgrading facilities bypipeline is disclosed, for example, in U.S. Pat. No. 6,096,192.

Bituminous heavy crudes, e.g. crude oils extracted from tar sands, showrelatively low API gravities. This is due to the very high residue(510+° C.) content of the bitumen. The lighter fractions in bituminousheavy crude usually are of a reasonable quality, although often of alesser quality than lighter fractions derived from the more conventionalcrudes, e.g. Arabian light or Brent oil. It is the sheer amount ofresidue that is the main cause for the low API gravity and consequentlythe high viscosity. This high viscosity results in the impossibility totransport the bitumen feed via pipelines.

Another problem of heavy bituminous crudes concerns the mismatch betweenthe demand of light products and their availability in the crude.Further, from a “standard refinery hardware point of view”, the use ofheavy bituminous will cause underloading of the part of the refinerythat processes the light fractions (e.g. <350° C.) and overloading thepart that processes the heavy fractions (e.g. >350° C.). This can beovercome by installing extra residue conversion capacity in therefinery. Another solution could be residue conversion capacity at thesource of the crude oil. However, conversion at the source comprisesusually “total residue conversion schemes”, which render all conversioncapacity useless at the receiving end of the crude, i.e. in the existingrefinery. Idle conversion capacity is a very unwanted situation, as mostof the invested capital has been invested in this very part of therefinery. As mentioned above, it is known to use solvents to transportheavy bituminous crudes, however, the use of the solvents (or diluents),usually implies that the solvent has to be returned to the productionplace.

A possible solution for the above problem is to separate the heavybituminous crude into a light and a heavy fraction and to thermallycrack (e.g. by means of visbreaking) the heavy fraction after which allliquid products are blended into a “synthetic” crude. This syntheticcrude has a lower viscosity and a lower residue (expressed as >510° C.)content. The drawback of such a scheme is that the asphaltenes in thethermally cracked residue have a lower stability, so when blending backthe lighter part of the crude into the total liquid product of thethermal cracker, stability problems may occur because of the poorpeptizing power (aromaticity or solvency) of these light fractions. Thismay result in a situation in which only restricted residue conversion ispossible, which in its turn will result in insufficient viscosityreduction.

3. SUMMARY OF THE INVENTION

In the present process, now, it is proposed to separate a heavybituminous feed into two parts, whereafter the first part of the feed isseparated into a light fraction and a heavy fraction, which heavyfraction is thermally cracked and separated in a second light fractionand a residual fraction, followed by mixing the two light fractions andthe second part of the feed into a pipeline-transportable crude oil,while the thermally cracked heavy fraction is used for the generation ofpower and/or heat. In this way a minimum upgrading is done at the sourceof the crude oil. This usually is an advantage, as the source is oftenin a remote location, often a harsh environment, little infrastructureand restricted availability of skilled labour. Further, by onlyconverting part of the heavy crude, i.e. thermal cracking of the heavyfraction obtained after distillation of part of the feed, a significantpart of the feed is untouched, which avoids to a large extent stabilityproblems when blending in light products into untouched heavy bituminouscrude. The split between untouched heavy bituminous crude and processcrude is such that a pumpable syncrude is produced, which fits muchbetter into the configuration of receiving refineries as well as in thedemand barrel of markets in which receiving refineries operate. Thepower and/or heat generated by conversion of the residual fractiondescribed above very suitably is to be used in the process of thepresent invention. Depending on the amount of power/heat generated,export may be possible. A very interesting possibility is the generationof electricity for export purposes.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple block flow diagram for an embodiment of the processfor the production of a pipeline-transportable syncrude.

FIG. 2 is another simple block flow diagram for an alternativeembodiment of the process for the production of a pipeline-transportablesyncrude.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention, now, relates to process for the production of apipeline-transportable crude oil from a bitumen feed, comprising;

(1) dividing the bitumen feed into two fractions, the first fractioncomprising between 20 and 80 wt % of the feed, the second fractioncomprising between 80 and 20 wt % of the total feed, (the two fractiontogether forming 100 wt % of the feed),

(2) distillation of the first fraction obtained in step (1) (preferablyunder vacuum) into a light fraction boiling below 380° C. (preferablythe 450−° C. fraction, more preferably the 510−° C. fraction) and aresidual fraction,

(3) thermal cracking (of at least part of, preferably all of,) theresidual fraction obtained in the distillation process described in step(2),

(4) distillation of the product obtained in step (3) into one or morelight fractions (boiling below 350° C.), optionally one or moreintermediate fractions (boiling between 350 and 510° C.) and a heavyfraction (boiling above at least 350° C.),

(5) combining the second fraction obtained in step (1), the lightfraction obtained in step (2) and the light fraction(s) obtained in step(4) to obtain a pipeline-transportable crude oil, and

(6) using heavy fraction obtained in step (4) for the generation ofpower and/or heat.

The bitumen feed may be described as a heavy bituminous crude. Thehydrogen/carbon atomic ratio is suitably between 1.3 and 1.6, usuallyabout 1.4 to 1.5.

The bitumen feed may comprise one single feed stream, but may alsocomprise several feed streams which are directly used for steps (2) and(5). In that case the feed stream of step (1) is to considered as thetotal feed stream of the individual streams.

The API gravity is suitably between 10 and 20 (heavy crudes), or,preferably less than 15, more preferably less than 10 (extra heavycrudes and, further especially, tar sands). The viscosity is usuallyabove 10,000 cps at reservoir temperature. These feeds may be producedfrom oil fields containing such heavy crudes, but suitable sources areshale oil and, especially, tar sands. Tar sands occur in a number ofplaces, notably Northern Canada (Athabasca tar sands) and Venezuela(Orinoco tar sands). A suitable separation between sand and oil may becarried out by hot water extraction (hot water extraction, steam/hotwater injection). The amount of asphaltenes in the feed is very high.

The pipeline-transportable crude oil as described may have to betransported over distances up till 1000 km or even above, usually uptill 500 km. The viscosity usually will be up till 500 cSt (@ 37.8° C.),preferably up till 250 cSt, more preferably up till 100 cSt.

The division of the total feed into the two fractions is suitablycarried out in such a way that the first fraction is as small aspossible while still a pipeline-transportable syncrude is obtained. Itwill be appreciated that the result will depend on the actualcomposition of the bitumen feed. A suitable division is between 20 and80 wt % of the total feed for the first fraction, preferably between 30and 70 wt %, more preferably between 35 and 60 wt %, of the total feed.

Distillation of the first fraction is carried out by conventional means.Atmospheric distillation in combination with vacuum distillation may beused. Also high vacuum flashing technology may be used. The lightfraction suitably contains all components boiling below 380° C.,preferably al components boiling up till 450° C., more preferably uptill 510° C. Using high vacuum flash technology, the light fraction maycontain all components boiling up till 600° C.

The thermal cracking may be done by a furnace cracking process, but ispreferably a soaker visbreaking process. In the soaker visbreakingprocess the feed is heated to a temperature suitably between 420 and490° C., preferably between 440 and 480° C., followed by furtherconversion in a soaker vessel. The residence time is suitably between0.5 and 2 hours. The conversion obtained may be between 4 and 14 wt % ofthe material boiling above 510° C., preferably between 8 and 12 wt %. Inthe case of furnace cracking the temperature is suitably between 440 and510° C., preferably between 480 and 500° C., the pressure is suitablybetween 5 and 50 bar, preferably between 15 and 20 bar and the residencetime is suitably between 1 and 15 minutes.

The product of the thermal cracking process is fed to a fractionater,preferably an atmospheric fractionater. Here the product is separatedinto two or more fractions. The light fraction suitably has a boilingpoint below 350° C., but up till 380°, or even 410° C. is possible. Theheavy fraction may be used for the generation of power and/or heat, or,preferably, is sent to a vacuum distillation unit, preferably a vacuumflash unit. In the latter option an intermediate stream is obtainedboiling between the boiling point of the light fraction and suitably atleast 450° C., preferably 510° C., more preferably 600° C. The veryheavy fraction obtained in this way is used for the generation of powerand/or heat. The intermediate fraction may be used as blending componentfor the pipeline-transportable crude oil.

In another embodiment of the invention the product of the thermalcracking process is first send to vapour liquid cyclone. The vapourproduct, at least comprising the compounds boiling below 400° C., isthen sent to the fractionater in the same way as described above, whilethe liquid stream is combined with the residual stream of thefractionater.

The pumpable syncrude according to the invention, now, is obtained bymixing the second fraction obtained in step (1), the light fractionobtained in step (2) and the light fraction obtained in step (4).Preferably also any intermediate fractions obtained in step (4) are usedin the blending process. This blending process is done by methods wellknown in the art, e.g. stirred or agitated vessel mixing, using jetmixers or mixing nozzles, line mixing, pump mixing etc.

In a further preferred embodiment of the process, the light fractionobtained is step (4) is hydrotreated. Hydrotreatment may be carried outby means of processes known in the art, especially catalytichydrogenation processes. Most of the unsaturates, suitably at least 80wt %, preferably at least 90 wt % are removed. Suitably some nitrogenand some sulphur present in the feed is removed. The removal of theolefins (di-olefins as well as mono-olefins) results in a more stableproduct.

In another embodiment of the invention the product of the thermalcracking process is first separated into two fractions, especially usinga quick separation step, for instance by using a vapour liquid cyclone.The vapour product, at least comprising the compounds boiling below 400°C., or even up till 450° C., is than sent to the fractionater andseparated into a light fraction (boiling below 350° C., but up till 380°C., or even 410° C. is possible) and one or more heavier fractions. Thelight fraction is used for the preparation of the pumpable syncrude,optionally after hydrogenation (see above). Optionally, an intermediatefraction may be obtained boiling between the boiling point of the lightfraction and 450° C., or even up to 500° C. Further, a heavy fraction isobtained which is combined with the liquid product obtained in thecyclone separation. The combined stream is sent to a distillation unit,preferably a vacuum flash unit, more especially an isenthalpic vacuumflash unit. A light fraction is obtained boiling up till 520° C., oreven up till 600° C. is obtained as well as a residual fraction. Theresidual fraction is used for the generation of power and/or energy. Thelight fraction, optionally combined with any intermediate fraction fromthe fractionator, is sent to a second thermal cracking unit. This may bea furnace cracker or a soaker visbreaking unit, preferably a furnacecracker. The condition used for the thermal cracking unit are atemperature between 440 and 510° C., preferably between 480 and 500° C.,and a pressure between 5 and 50 bar, preferably between 15 and 30 bar.

The product of the second thermal cracking unit is sent to thefractionater described above.

The generation of power and/or heat from the residual stream asdescribed above may be done by using equipment and processes well knownin the art. For instance reciprocating engines (e.g. steam engines,internal combustion engines), steam turbines, and expansion turbines maybe used. See for instance, Perry's Chemical Engineer's Handbook, SixthEdition, Chapter 9.

The invention further relates to a syncrude obtainable by any of theprocesses described above.

Referring to FIG. 1, a bitumen feed is split into a first fractioncomprising between 25 and 75 wt % of the total feed and a secondfraction comprising between 75 and 25 wt % of the total feed. The firstfraction is sent to crude distillation unit/high vacuum unit 2, andseparated into a 510−° C. fraction and a 510+° C. fraction. The 510+° C.fraction is sent to visbreaking unit 3. The 350+° C. fraction out of thevisbreaking unit process is sent to vacuum flash unit 4. The 520+° C.fraction of the product of the vacuum flash unit is used for thegeneration of power and/or heat. The 510−° C. fraction from the crudedistillation unit/high vacuum unit 2, the 350−° C. fraction fromvisbreaking unit 3, optionally after bulk hydrotreatment to removeolefins and some removal of sulphur and nitrogen in hydrotreatment unit5, and the 350-520° C. fraction from vacuum flash unit 4 are blendedinto the second fraction of the feed.

Referring to FIG. 2, a bitumen feed is split into a first fractioncomprising between 25 and 75 wt % of the total feed and a secondfraction comprising between 75 and 25 wt % of the total feed. The firstfraction is sent to crude distillation unit/high vacuum unit 2, andseparated into a 510−° C. fraction and a 510+° C. fraction. The 510+° C.fraction is sent to visbreaking unit 3. After quick separation of theproduct stream of the visbreaking process the 400−° C. fraction is sentto fractionator 4.

The 400+° C. fraction of the visbreaking process is sent to vacuum flashunit 5. The residual fraction of the vacuum flash unit is used for thegeneration of power and/or heat. The 400-520° C. fraction of vacuumflash unit 5, together with the 350-500° C. fraction from fractionator 4is sent to high severity thermal cracking unit 6. the converted productfrom high severity thermal cracking unit 6 is sent to fractionator 4.The bottom fraction of fractionator 4 is sent to vacuum flash unit 5.The 510− fraction of crude distillation unit/high vacuum unit 2,together with the 350−° C. fraction of fractionator 4, optionally afterbulk hydrotreatment to remove olefins and some removal of sulphur andnitrogen in hydrotreatment unit 7, are blended into the second fractionof the feed.

1. A process for the production of a pipeline-transportable crude oilfrom a bitumen feed, the process comprising; (1) dividing the bitumenfeed into two fractions, the first fraction comprising between 20 and 80wt % of the feed, the second fraction comprising between 80 and 20 wt %of the total feed, the two fractions together forming 100 wt % of thefeed; (2) distilling of the first fraction obtained in step (1) into alight fraction boiling below 380° C. and a residual fraction; (3)thermal cracking of at least part of the residual fraction obtained inthe distillation process described in step (2); (4) distilling of theproduct obtained in step (3) into one or more light fraction(s) boilingbelow 350° C., optionally one or more intermediate fractions boilingbetween 350 and 510° C. and a heavy fraction boiling above at least 350°C.; (5) combining the second fraction obtained in step (1), the lightfraction obtained in step (2) and the light fraction(s) obtained in step(4) to obtain a pipeline-transportable crude oil; and, (6) using theheavy fraction obtained in step (4) for the generation of power and/orheat.
 2. The process according to claim 1, in which the bitumen feed instep (1) is divided into two fractions, the first fraction comprisingbetween 40 and 60 wt % of the feed and the second fraction comprisingbetween 60 and 40 wt % of the total feed.
 3. The process according toclaim 2, in which the thermally cracked product is split by distillationinto a light fraction boiling below 350° C., an intermediate fractionboiling between 350 and 510° C. and a heavy fraction boiling above 510°C.
 4. The process according to claim 3, in which at least part of theintermediate fraction is also added to the pipeline-transportable crudeoil of step (5).
 5. The process according to claim 4, in which theintermediate fraction is thermally cracked, followed by distillationinto a light product and a heavy product, the light product being addedto the pipeline-transportable crude oil mentioned in step (5), and theheavy product being used in the generation of power and/or heat asdescribed in step (6).
 6. The process according to claim 1, in which thethermal cracking in step (3) is carried out at a temperature between 440and 510° C. and a pressure between 5 and 50 bara.
 7. The processaccording to claim 1, in which the thermal cracking in step (3) iscarried out in a soaker vessel.
 8. The process according to claim 7, inwhich the thermal cracking is carried out at a temperature between 420and 500° C. and a pressure between 2 and 20 bara.
 9. The processaccording to claim 1 in which the first fraction obtained in step (1) isdistilled unto a light fraction boiling below 450° C. and a residualfraction.
 10. The process according to claim 2 in which the firstfraction obtained in step (1) is distilled unto a light fraction boilingbelow 510° C. and a residual fraction.
 11. The process according toclaim 3 in which all of the intermediate fraction is added to thepipeline-transportable crude oil of step (5).